From Bulbapedia, the community-driven Pokémon encyclopedia.
Diane (Japanese: ダイアン Diane) is an anime character who appeared in Jirachi: Wish Maker. She assists her childhood friend, Butler, in his magic show. Her Japanese voice actress is Riko Mahise and her English voice actress is Megan Hollingshead.
Diane originally was friends with Butler and hated the fact that he joined Team Magma. However, she hated the fact that he stole Jirachi even more, because he thought she wanted it.
When the fake Groudon was rampaging, she was the first human after Team Rocket to get swallowed up. She was later released.
Along with Butler, Diane had a cameo during the credits of the eighth movie, and appeared in Pokémon Diamond and Pearl as a Cool Trainer on Route 229, though the reference was not caught by the English localization team.